Blood vessel valves include flexible tissue leaflets that passively alternate between open and closed positions as the forces of a blood stream act upon them. As blood flows in a first direction, the leaflets are urged apart from each other, and allow the blood to pass. Between pulses, as the blood attempts to flow in a reverse direction, the blood acts upon upstream surfaces of the individual leaflets, causing the leaflets to move inwardly. As the leaflets move inwardly, the edges of the individual leaflets (two, in the case of bicuspid valves, and three in the case of tricuspid valves) abut against each other, effectively blocking the blood flow in the reverse direction.
Valves are also present within the heart. The heart contains four one-way valves that direct blood flow through the heart and into the arteries. Three of these valves, the aortic valve, the tricuspid valve, and the pulmonary valve, each have three leaflets. The fourth valve, the mitral valve, has two leaflets. By defining a direction in which blood can flow, these valves are responsible for the resulting pump effect a heart has on blood when the heart beats.
A number of diseases result in a thickening, and subsequent immobility or reduced mobility, of valve leaflets. Valve immobility leads to a narrowing, or stenosis, of the passageway through the valve. The increased resistance to blood flow that a stenosed valve presents eventually leads to heart failure and death.
Treating severe valve stenosis or regurgitation has heretofore involved complete removal of the existing native valve followed by the implantation of a prosthetic valve. Naturally, this is a heavily invasive procedure and inflicts great trauma on the body leading usually to great discomfort and considerable recovery time. It is also a sophisticated procedure that requires great expertise and talent to perform.
Historically, such valve replacement surgery has been performed using traditional open-heart surgery where the chest is opened, the heart stopped, the patient placed on cardiopulmonary bypass, the native valve excised and the replacement valve attached. More recently, it has been proposed to perform valve replacement surgery percutaneously, that is, through a catheter, so as to avoid opening the chest.
One such percutaneous valve replacement method is disclosed in U.S. Pat. No. 6,168,614 (the entire contents of which are hereby incorporated by reference) issued to Andersen et al. In this patent, the prosthetic valve is collapsed to a size that fits within a catheter. The catheter is then inserted into the patient's vasculature and moved so as to position the collapsed valve at the location of the native valve. A deployment mechanism is activated that expands the replacement valve against the walls of the body lumen. The expansion force pushes the leaflets of the existing native valve against the lumen wall thus essentially “excising” the native valve for all intents and purposes. The expanded structure, which includes a scaffold configured to have a valve shape with valve leaflet supports, is then released from the catheter and begins to take on the function of the native valve. As a result, a full valve replacement has been achieved but at a significantly reduced physical impact to the patient.
One particular drawback with the percutaneous approach disclosed in the Andersen '614 patent is the difficulty in preventing leakage around the perimeter of the new valve after implantation. Since it appears that the tissue of the native valve remains within the lumen, there is a strong likelihood that the commissural junctions and fusion points of the valve tissue (as pushed against the lumen wall) will make sealing of the prosthetic valve around the interface between the lumen and the prosthetic valve difficult. Furthermore, in some patients, the deflection of the leaflets against the lumen walls could potentially obstruct the ostial openings of the lumen.
Although both the traditional open heart valve replacement surgery and the newer percutaneous valve replacement surgery replace a native valve in entirely different ways and both have their drawbacks, the paradigm of these two approaches is identical: Render the native valve useless, either through excision (open heart) or immobilization (percutaneous), and then implant a completely new replacement prosthetic valve to take over. In other words, both approaches rely entirely on the premise that the native valve must be entirely replaced (physically or functionally) by an entirely new prosthetic valve.
In contravention of the prior art, the present invention introduces an entirely different paradigm to valve replacement surgery, something neither taught nor contemplated by the open heart approach or the percutaneous approach (e.g., U.S. Pat. No. 6,168,614) and something that largely avoids the drawbacks associated with both. More specifically, the present invention is premised on leaving the native valve in place, not on its excision or immobilization, and then utilizing the native valve as a platform for actually treating the diseased valve. This is a wholly new approach to treating diseased valves.
For example, in one embodiment of the invention, the physician diagnoses that the patient has a stenotic valve and then percutaneously mounts a plurality of small “leaflet valves” or “mini-valves” on one or more of the diseased native valve leaflets. In other words the native valve and its leaflets are used as a planar surface or a type of “bulkhead” on which new mini leaflet valves are mounted. The native valve remains in place but valve disfunction is remedied due to the presence of these new leaflet valves. As a result, the diseased valve is successfully treated without the complication associated with removing the native valve.
This leads to a much simpler and safer approach as compared to the prior art. It avoids the invasive nature of the open heart approach and avoids the sealing and ostial blockage problems of the percutaneous approach.